1. Field of the Invention
The present invention relates to countermeasures and more, particularly, to a method and apparatus for creating coherent sources of radiation that can be used for decoying hostile missiles of the infrared xe2x80x9cheat-seekerxe2x80x9d type away from the target vehicle being protected and for attenuating Laser beams directed at the vehicle.
2. Description of the Prior Art
It is increasingly common practice in missile operations to provide guidance means on the missile itself to enable it to xe2x80x9chome-inxe2x80x9d on its target. A number of types of missiles are presently designed to incorporate means which enable them to xe2x80x9cseek-outxe2x80x9d a particular moving target by homing-in on the infrared energy emitted by latter. Missiles of this type are effective against targets such as aircraft and surface vehicles which emit various amounts of infrared radiation from their propulsion systems.
A number of techniques have been proposed to protect the target vehicle against heat-seeking missile threat. These include: electronic jammers, suppressants, shields, and blocking devices, pyrophorics, and flares.
The typical electronic jammer is designed to emit signals at frequencies which will adversely affect the processing of guidance intelligence in the IR missile seeker. For the system to be effective, however, the processing mechanism of the IR seeker must be known and the missile processing frequencies must be fairly uniform; thus electronic jamming has obvious disadvantages.
Suppressants are additives either injected into the hot exhaust gases or introduced between the gases and the oncoming IR seeking missile. Because of the large quantities of additives required to achieve any significant IR emission reduction and because of other drawbacks, the technique has limited capabilities and is considered to be impractical.
Properly designed and installed shields and blocking devices used to screen the IR emissions of the target vehicle from the heat-seeking guidance means can increase vehicle survivability but pose a weight and drag penalty on the vehicle. Lack of protection against certain types of xe2x80x9cplume-seekingxe2x80x9d missiles and the possibility that the shielding obtained is above the missile lock-on level are other major disadvantages.
Pyrophorics have been used to produce a fireball near the target vehicle to thereby decoy a hostile missile away from its intended target. Pyrophorics, such as triethylaluminum, mixed with jet fuel result in mixtures having a high hydrocarbon content such that the flame for decoy purposes has a substantial IR output in the spectral range of interest. Because pyrophorics are highly reactive, an ignition system probably will not be required within certain aircraft altitude and velocity limits. However, the high reactivity of pyrophorics makes them hazardous to handle and store aboard the vehicle. The technique also introduces weight and cost penalties.
Flares ejected from the target with an object of decoying a hostile missile have been extensively utilized for IR countermeasures because even a two-pound unit can provide up to 10-seconds protection against IR-seeking missiles. In as much, however, as the typical flare presently used burns a magnesium-teflon powder whose relative IR intensity is more pronounced in the lower wave-lengths, it is possible to fit the seeker with filter means such that the missile discriminates against the flare-predominant wavelengths and homes in on the wave-lengths produced by the vehicle propulsion combustion-products.
In the prior art, also, S. E. Lager, U.S. Pat. No. 3,150,848, discloses a method for decoying a missile from its intended target, which method employs a pyrophoric in the phyrophorics countermeasures technique disclosed above except that an oxidizer is used instead of jet fuel in the mixture ejected from the target. Inasmuch as Lager uses, in his method, a typical pyrophoric which is capable of spontaneous ignition when exposed to air, the technique disclosed is open to question with respect to safety in handling, storage and use.
Also disclosed in the prior art by G. W. Goddard, U.S. Pat. No. 2,895,393, is a system for igniting the fuses of flares dropped into the exhause nozzle of a jet or rocket propelled aircraft and ejecting the flares therefrom such that, after suitable delay, the flares are xe2x80x9cexplodedxe2x80x9d to emit radiant energy. Although the system of Goddard is intended to provide illumination in an aerial photography system rather than to act as a countermeasures means against hostile missiles, Goddard is of interest as disclosing an example of the dispersion of flares from an aircraft.
The subject invention comprises a method and apparatus for use therewith for creating coherent sources of radiation that can be used for various purposes such as for-protecting aircraft and other vehicles from hostile missiles equipped with guidance systems of the infrared heat-seeking type and from high-power Laser beams and Laser radar. In the method, a number of sources of radiation are dispersed controllably from the target vehicle, for missile countermeasures, each of the sources is capable of emitting infrared energy comparable in wave length and intensity to that radiated by the target vehicle itself such that the hostile missile will be decoyed away from its intended target by the spurious radiation sources. For Laser countermeasures, the coherent sources of radiation are interposed in the path of the Laser beam such that the effectiveness of the beam is degraded by combustion products in the radiation sources. The radiation sources of this method are produced by the target vehicle by withdrawing a small quantity of fuel from the fuel tank, adding a gelling agent to the xe2x80x9cchargexe2x80x9d of fuel such as to create a fuel gel and thereby add to the coherence of the charge, and then simultaneously igniting and ejecting the charge in the form of a ball of flame with extended burn time.
In all the prior art decoy-type countermeasures using a spurious radiation source technique related to that of the subject invention, there is a requirement for the vehicle being protected to carry either a quantity of pyrophoric materials or a number of flares. Further, the quantity of pyrophoric or the number of flares is dependent on the nature and duration of the vehicle mission. It will be seen, therefore, that the vehicle is loaded with countermeasures equipment and stores for a particular number of decoy operations and the weight penalty for the mission is fixed even if there is no requirement for decoy operation during the mission. Thus, when the vehicle is not exposed to a missile threat during a mission the full weight of the unused pyrophoric or flare-type countermeasures stores as well as the equipment for dispensing the stores represent a cost and performance penalty on the vehicle. In the subject method, however, the spurious radiation produced for decoy purposes is generated by the burning of a mixture composed of a small quantity of fuel from the vehicle""s tank and a gelling agent. The penalty on the vehicle is the weight of the equipment used to form, ignite, and eject the burning mixture and of the gelling agent, since the fuel set aside for decoy operations, if not expended, can be used to extend the flight time of the vehicle or to enhance its reserve factor. Inasmuch as only about five percent by weight of gelling agent is used with a one-pound charge of fuel, the payload weight penalty for the countermeasures equipment and stores is less by a factor of 3 or 4 than the prior art IR decoy techniques.
The fireballs produced in this countermeasures method can also be used by both airborne and surface vehicles for protection against high-power Laser weapons and Laser radars. The burning fuel gell particles and other combustion products of the fireballs when interposed in a Laser beam create a variety of beam degradation effects. With fuels usually used, the major, products of combustion such as CO2 and H2O have a high attenuation on Laser beams of particular wavelengths of interest, particularly 10.6 microns. Since complete combustion of the fuel gel generally does not occur, a variety of intermediate products, as well as carbon particles, will be formed. Laser beam scattering effects will be produced by the carbon particles, which will occur in a variety of sizes. Intermediate products created will have an absorption effect on Laser beams at various wavelengths. For example, an intermediate product created when gelled jet fuel is burned is ethylene which is a high absorber of the 10.6 micron wavelength of a Laser beam.
The present invention thus provides a radiation-type countermeasures method in which fuel from the vehicle being protected instead of extraneous pyrophoric material or flares is used to generate countermeasures radiation such that the cost and performance penalty on the vehicle is minimized.
It is a further object of this invention to provide a radiation decoy-type countermeasures system substantially not requiring the use of pyrophoric materials or flares such that the hazards associated therewith during storage, handling, and operation are substantially eliminated.
It is another object of this invention to provide a radiation-decoy type countermeasures in which the bandwidth of IR emissions from the decoy radiation simulates closely the bandwidth or IR xe2x80x9csignaturexe2x80x9d of the vehicle engine and in which said decoy radiation is of a substantially higher intensity to enhance the successful decoying of the hostile missile.